In the quest to improve fuel economy, increase performance and/or reduce various emissions of internal combustion engines, there has been considerable development of fuel injectors, and particularly electromagnetically operated injectors for spark-ignited engines. One relatively common provision is that of delivering excess liquid fuel to the injector, and returning the unused portion of the fuel to the fuel tank for reuse. This provision is often made to impart a swirling motion to the fuel prior to opening the valve and injecting the fuel into the engine, as discussed in U.S. Pat. No. 3,241,768 issued to Croft and in U.S. Pat. No. 4,179,069 issued to Knapp et al. In U.S. Pat. No. 4,232,830 to Casey et al, fuel entering the injector is "circulated through the interior of the injector jacket", presumably for subsequent injection and possibly for component-cooling purposes, and the remainder is returned to the fuel tank.
However, in addition to the aforementioned reason for returning a portion of the fuel from the injector to the fuel tank, further advantages may be derived if that return-fuel can also transport vapors from the injector. Such vapors are often formed in the region of the valve and the spray nozzle as a result of the engine heat. These vapors may inhibit the accurate metering of fuel to the engine.
The aforementioned Knapp et al patent provides a path for returning fuel from the injector to a tank only while the valve is closed. However, when the valve is open that return path is closed. This intermittent opening and closing of the return path introduces undesirable pressure pulses at the valve, particularly if a pressure regulator is located in the fuel line downstream of the injector.
The injectors of the aforementioned Croft and Casey et al patents each provide a flow path which is continuous from the injector inlet to the return outlet, even during an open-valve condition. However, the geometry and sizing of those paths is not well suited to the removal of vapors from those injectors.
Accordingly, it is a principal object of the present invention to provide a fuel injector having a continuous fuel return path for effectively and substantially completely removing vapors from the injector.
It is a further object of the invention to provide such a continuous fuel return path which additionally cools the magnet motor of an electromagnetic operated injector.
In accordance with the present invention, there is provided an electromagnetically operated fuel injection valve structured to include a housing having a fuel inlet opening, a fuel discharge opening and a fuel return opening, there being a continuous liquid path from the inlet opening to the return opening and an intermittent, or valved, liquid path from the inlet opening to the discharge opening. The injector is intended for use in a predetermined spatial orientation with an internal combustion engine and the return opening is located to be elevationally at least as high as the remainder of the continuous liquid path to facilitate removal of vapor appearing in the injector. The continuous liquid path has a slope, in the direction of flow toward said return opening, which preferably is always 0 to positive relative to a horizontal axis or plane.
A discharge valve is provided in the injector and exists in the valved path. The continuous path and the valved path coincide between the inlet opening and the valve. The valved path also has a slope which is preferably always 0 or positive relative to a horizontal axis or plane, viewed from the discharge opening toward and to the region of coextensively of the paths. The continuous path and the valved path are sized such that the liquid flow in the continuous path when the valve is closed is preferably at least 1.5-2 times that in the valved path when the valve is full open for adequate removal of generated vapors, yet is not so great as to cause excessive weathering of the fuel.
The discharge valve is connected to an armature which is in turn actuated by a solenoid comprised of a coil, a tubular bobbin and an electromagnetic frame. The frame has a vertical tubular core portion and an upper flange extending outwardly therefrom. The coil is disposed on the bobbin and the bobbin is coaxially disposed about the frame core portion below the flange. The flange, and preferably also the core of the frame include a slot or opening extending therethrough. The continuous liquid path extends upwardly through the frame tubular core and, in parallel, through the opening in the upper flange. In a preferred embodiment, the return opening in the housing is located coaxially above the tubular frame of the solenoid.